The present invention relates generally to washable, polymerizable compositions. More particularly, the present invention relates to such compositions curable through mechanisms, anaerobic and heat, for use as impregnation sealants.
Impregnation sealing of porosity in porous parts frequently is carried out by introducing sealant compositions into the porosity under a pressure differential, by vacuum techniques which are well known in the art.
Sealant compositions typically employed in these impregnation applications include a wide variety of self-curing anaerobic sealants, e.g., the compositions described in U.S. Pat. Nos. 3,672,942; 3,969,552; Re. 32,240; and U.S. Pat. No. 4,632,945, which are curable through free-radical polymerization in the presence of suitable free-radical initiators, e.g., peroxy-type initiators, as well as thermal-curing sealants, e.g., the compositions described in U.S. Pat. Nos. 4,416,921 and 4,416,921, as well as sealants which cure by both anaerobic and heat cure mechanisms.
One problem common to many impregnation sealants is the accumulation of excess sealant on the outer surface of parts. Excess sealant is removable by normal abrasion or by contact with various liquids. The removal of extraneous or surface accumulation of anaerobic and heat curing sealants from the parts is important because such residues can readily contaminant the environment of porous parts. In addition, such surface sealant deposits may, by virtue of their thickness, cause the impregnated product part to vary from the desired dimensional specifications. This often renders the part deficient or even useless for its intended function in applications requiring close dimensional tolerances.
Furthermore, such surface sealant deposits may interfere with subsequent painting, plating, or assembly operations or cause delamination of applied paint or plated films which frequently are performed on porous articles subsequent to their impregnation. Specifically, such surface sealant deposits may be removed during painting or plating operations, resulting in contamination of the baths used in such operations, and may interfere with the adhesion of paint, plating, and the lie to the impregnated part.
To remove excess sealant from impregnated articles, agitated rinse times of significant duration are required. The actual rinse time will depend upon, among other things, the nature of the article, such as porosity, and the washability of the uncured sealant in an aqueous solution. Often such rinse operations are from about five to about twenty minutes, but actual rinse times for any particular article may be even longer in duration. In addition, chemicals, such as surfactants or detergents, may also be added to the aqueous solution to facilitate the removal of sealant deposits.
For example, U.S. Pat. No. 3,672,942 to Neumann et al. discloses an anaerobic impregnant comprising a free-radical polymerizable acrylate ester monomer and free-radical polymerization initiator, which requires an organic solvent, such as a halogenated hydrocarbon, to remove uncured impregnant from the outer surface of a porous article.
U.S. Pat. No. 3,969,552 to Malofsky et al. describes a washing process for removing excess impregnant from the surface of the porous article after porosity impregnation. The disclosed impregnation composition comprises an acrylic anaerobic curing resin and a peroxy initiator therefor. The wash solution is an aqueous solution of a nonionic surfactant of specified formula which is necessary for the removal of uncured impregnant.
U.S. Pat. No. Re. 32,240 to DeMarco describes a self-emulsifying anaerobic composition for porosity impregnation applications, comprising an anaerobically curing monomer such as an acrylic ester, a peroxy initiator therefor, e.g., a hydroperoxide or perester, an anionic or nonionic surfactant which is dissolved in the composition and renders it self-emulsifying upon mixing with water.
U.S. Pat. No. 5,256,450 to Catena describes an anaerobic polymerizable acrylate composition which requires a mixture of three different polymerizable acrylates in specific amounts to obtain a composition that cures and rinses without the use of organic solvents or surfactants.
The above-described anaerobic sealant compositions are typically impregnated into the porosity of metal parts by vacuum and pressure techniques. A vacuum removes air from the porosity of the metal parts. Sealant compositions are then introduced into the porosity under a pressure differential using ambient pressure or elevated pressure conditions. After impregnation, an operation, such as a centrifuge operation, removes excess surface sealant from the metal part. Even after such removal of gross surface accumulations of the impregnant, there is a significant amount of impregnant at the surface of the porous articles, particularly in the vicinity of the pores. When the impregnant is anaerobically cured, the aforementioned surface accumulations as well as the outermost layer of the impregnant in the pores of the article, particularly shallow surface pores, are in contact with oxygen, so that such surface quantities of the impregnant are uncured or only partially cured.
Remaining surface sealant or sealant trapped in blind holes of the impregnated parts is typically removed in an agitated water rinse zone. The impregnated and water-rinsed parts may be transferred to an activator zone in which the impregnated parts are contacted with a catalyst activator solution, to effect curing of the sealant material at the entrance to the pores in the parts. This creates a hardened plug or cap of sealant material in the outer portion of the pore, trapping the resin for anaerobic self-cure.
Thereafter, the impregnated parts may be transferred to a final rinse zone for removal of the activator solution from the impregnated parts. This final rinse solution may be at elevated temperature, e.g., on the order of about 50xc2x0 C., to warm the impregnated parts for quick drying, and to accelerate curing of the anaerobic impregnant within the interior porosity of the article, the rate of such cure increasing with increasing temperature.
As a variation on the above-described impregnation system, it is known to utilize a heat-curing resin in place of the anaerobically-curing resin, whereby the activating and final rinsing steps previously described are eliminated in favor of a hot rinse final step. In the heat-curing resin impregnation system, after impregnation and rinsing of excess surface material, the parts are contacted with hot water at temperatures on the order of about 50xc2x0 C. to about 90xc2x0 C. to cure the impregnant resin.
Among the previously developed heat-curing impregnating compositions for sealing porous parts are the compositions disclosed in the patents identified and discussed below.
U.S. Pat. No. 4,416,921 to Dunn describes a heat-curing sealant composition which contains a polymerizable acrylic monomer, an azonitrile and an anionic or nonionic surfactant to render the composition self-emulsifying upon mixing with water.
U.S. Pat. No. 4,147,821 to Young describes a heat-curing sealant composition which contains (meth)acrylic monomer and a polyfunctional acrylic monomer. An emulsifier is required to aid in the rinsing of uncured sealant from the surface of a porous article.
Once the heat-curable impregnant composition is introduced into the porosity of the parts to be sealed, the parts are transferred to an agitated water rinse zone for removal of any remaining surface accumulations of sealant or extraneous sealant which is trapped in blind holes of the impregnated parts. After removal of the excess sealant in the agitated water rinse zone, the impregnated parts are passed to a tank containing hot water, e.g., at a temperature of 90xc2x0 C. to 150xc2x0 C., or other medium at elevated temperature which serves to cure the sealant composition in the porosity. Relative to anaerobic impregnant compositions, heat-curable impregnant compositions may be effectively used with a minimum of monitoring and maintenance, with little or no aeration being required.
In all of the above-described impregnation compositions and systems, either organic solvents or specific surfactants are used to remove uncured sealant in a reasonable rinse time or specific multi-component sealant compositions are used to avoid excessive rinse times.
Accordingly, there is a need to provide a heat-curable and/or an anaerobic impregnating sealant without these and other disadvantages.
The present invention provides washable compositions for sealing porous articles which have improved washability characteristics and reduced rinsing requirements. The present compositions achieve lower rinse times while producing improved surface cleaning of uncured polymer. The compositions of the present invention demonstrate utility in the sealing and/or aqueous rinsing operations, and obviate the conventional use of multi-component cleaning systems.
In particular, the present invention provides a sealant composition with improved washability, thereby reducing the rinse duration, improved ease of use by eliminating the need for specific surfactants, and which improve surface cleanliness of the porous article.
In one embodiment of the present invention, the inventive composition includes a curable (meth)acrylate glycerol, and is self-emulsifying upon mixing with water to facilitate aqueous rinsing of uncured composition. The inventive composition further includes curing initiators and curing accelerators to promote anaerobic or thermal curing through free radical mechanisms.
In another embodiment of the present invention, the invention composition includes a polymerizable composition and further includes a compound selected from the group consisting of glycerol, oxylated glycerol, (meth)acrylate glycerol and combinations thereof which improve the washability of the inventive sealants in aqueous solutions.
In one desirable embodiment, the inventive composition contains an (meth)acrylate glycerol which has at least one terminal (meth)acrylate group to allow crosslinking of the meth)acrylate glycerols upon curing.